Specially because, if he was the son of Sestius, why was his name Cornelius Scipio?
Here comes Caius Suetonius Tranquillus, Vita Divus Iulius, cp. LIX, sec. II:
Ad eludendas autem vaticinationes, quibus felix et invictum in ea provincia fataliter Scipionum nomen ferebatur, despectissimum quendam ex Corneliorum genere, cui ad opprobrium vitae Salvitoni cognomen erat, in castris secum habuit.
"Furthermore, to make the prophecies ridiculous which declared that the stock of the Scipios was fated to be fortunate and invincible in that province, he kept with him in camp a contemptible fellow belonging to the Cornelian family, to whom the nickname Salvito had been given as a reproach for his manner of life".
And here comes Lucius Mestrius Plutarchus, Caesar, cp. LII, sec. IV-V:
"On learning that the enemy were emboldened by an ancient oracle to the effect that it was always the prerogative of the family of the Scipios to conquer in Africa, he either flouted in pleasantry the Scipio who commanded the enemy, or else tried in good earnest to appropriate to himself the omen, it is hard to say which. He had under him, namely, a man who otherwise was a contemptible nobody, but belonged to the family of the Africani, and was called Scipio Sallustio. This man Caesar put in the forefront of his battles as if commander of the army, being compelled to attack the enemy frequently and to force the fighting".
And here comes Cassius Dio, Historia, Liber XLII, cp. LVIII, sec. I:
"When Caesar learned of this and saw that his own soldiers also were persuaded that it was so and were consequently afraid, he added to his retinue a man of the family of the Scipios who bore that name (he was otherwise known as Salutio)".
The orthography of his agnomen varies considerably among the diverse translations of these sources.